1. Field of the Invention
The present invention relates to a small electrostatic capacitance probe device for use in measurement of micro-bore diameter and measurement of surface roughness and to a displacement measuring circuit using the probe device.
2. Description of the Related Art
Recent developments in precise machining technologies permit processing of micro-bores (or holes) with inner diameters of 100 xcexcm or less to be applied in many fields. These micro-bores occupy important elements in actual products while the conventional bore size evaluation is already difficult at a stage of sub-millimeter in practice. Therefore, a precise evaluation technology for micro-bore diameters is required.
For such the requirement, there is a remarkable technology for producing a micro-cantilever structure using fine patterning technologies for silicon. This silicon cantilever structure can be employed as an electrical switch, that is, a displacement probe for detecting electrical conduction when it contacts with a work to be measured.
A contact probe using the above-described silicon cantilever structure is unstable in electrical conduction and difficult to perform a high precise measurement because a contact portion is unstable.
The present invention has been made in consideration of the above situation and accordingly has an object to provide a small, high-performance electrostatic capacitance probe device and a displacement measuring circuit using the probe device.
The present invention provides an electrostatic capacitance probe device formed from a processed, stacked substrate, which includes a first semiconductor substrate and a second semiconductor substrate stacked thereon via an insulator. The probe device comprises a support substrate formed by etching the first semiconductor substrate to remove undesired portions; a probe formed by etching the second semiconductor substrate and provided with a proximal electrode portion secured on the support substrate by means of the insulator and a beam portion separated from the support substrate by removing the insulator from beneath the beam portion; and a pair of detecting electrodes formed by etching the second semiconductor substrate, secured on the support substrate by means of the insulator, located to sandwich a part of the beam portion close to the proximal electrode portion, and having sides capacitively coupled with sides of the beam portion. Deformation of the tip of the probe caused from contact with a work is detected from a differential capacitance variation between the probe and the pair of detecting electrodes.
The electrostatic capacitance probe device according to the present invention employs a stacked substrate with a semiconductor substrate/insulator/semiconductor substrate structure, which is processed to integrally form a probe having an end secured on a support substrate and a pair of detecting electrodes capacitively coupled with sides of the probe. Conventional fine patterning technologies for semiconductor devices can be utilized for processing the stacked substrate to obtain a small probe device. The use of lateral etching of a ground insulator during the process of the substrate can remove the ground insulator from beneath the elongated beam portion of the probe while remaining the ground insulator beneath the proximal electrode portion with a larger area. Thus, the probe except for the proximal electrode portion can be easily processed in a state floating from the support substrate.
In the present invention, the principle of probe contact detection is to detect decomposition of the tip (distortion of the beam portion) of the probe caused from contact with a work to be measured. The decomposition can be detected from a differential capacitance variation between the probe and the pair of the detecting electrodes (that is, between the proximal electrode portion and the pair of the detecting electrodes). Such the differential processing allows a high precise contact detection to be performed without any affection from capacitance variations due to temperature variations and from variations of absolute electrostatic capacitance values due to variable manufacture conditions. Therefore, a small, high-performance probe device optimal for measurement of a micro-bore diameter can be obtained.
Preferably, the electrostatic capacitance probe device according to the present invention may further comprise an auxiliary electrode portion formed by etching the second semiconductor substrate, secured on the support substrate by means of the insulator, and having sides capacitively coupled with sides of the proximal electrode portion. A capacitor between the auxiliary electrode portion and the proximal electrode portion may be employed as a negative feedback capacitor for a displacement measuring circuit arrangement.
Preferably, capacitive coupling portions between the pair of detecting electrodes and the beam portion, as well as a capacitive coupling portion between the auxiliary electrode portion and the proximal electrode portion, may be formed in the form of interdigitating fingers. This arrangement increases coupling capacitance even in a small device and allows for contact (displacement) detection with high precise and reduced affection from noises.
A displacement measuring instrument may be configured using the above electrostatic capacitance probe device. In this case, the displacement measuring instrument comprises an alternating signal source for complementarily driving the pair of detecting electrodes; and a signal processing circuit for detecting an amplitude value of a signal appeared on the proximal electrode portion.
A displacement measuring instrument may also be configured using the electrostatic capacitance probe device having the auxiliary electrode portion. In this case, the displacement measuring instrument comprises an alternating signal source for complementarily driving the pair of detecting electrodes; a signal processing circuit for detecting an amplitude value of a signal appeared on the proximal electrode portion; and a negative feedback circuit for taking an output from the signal processing circuit through an analogue switch in synchronization with the alternating signal source and feeding it to the auxiliary electrode.
Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof.